Metal matrix composite (MMC) have found application in many areas after being developed, 50 years ago. MMC was primarily, developed for rough applications, such as for space and for rocket applications. Typical requirement are; high temperature capability, high thermal conductivity, low coefficient of thermal expansion, and high specific stiffness and strength.
MMC, consist of a metallic binder and a ceramic filler. Metallic binders provide high thermal conductivity and toughness to the MMC and the ceramic filler provide strength, hardness and wear resistance to the MMC.
MMC can be produced by many different techniques, melting metallurgical processes, powder metallurgical processes and hot isostatic pressing. By altering the manufacturing method, the processing and the finishing, as well as by the form of the reinforcement components, it is possible to obtain different characteristics, although the same composition and amounts of the components are involved.
A common type of MMC consists of aluminium as binder and silicon-carbide as filler. Strength, hardness properties of the aluminium based MMC can be tailored by adjusting shape and amount of the silicon carbide particles.
One application where the MMC has been successfully applied is gun barrels. The use of propellants in guns for firing high energy projectiles in rapid and long burst cycles generate very high flame temperatures, which cause high erosion of conventional steel material. The erosion will limit the lifetime of gun barrels significantly to unacceptably short times. US 2005268517 describe a solution where the inside of a barrel is covered with a ceramic composite liner with metal matrix composite.
Another application is gas exhaust nozzles. Gas exhaust nozzles must withstand high speed gases with very high temperature and pressure gradients and at the same time meet economic, weight and noise goals. The use of an advanced material such as MMC, will reduce weight and extend lifetime of a nozzle component compared to a conventional steel material. In addition to the flow of high-temperature exhaust gases into the gas nozzle, ambient air may in some applications be entrained to reduce gas exit velocities and suppress sound. This will lead to extremely high temperature gradients and, hence, high thermal stresses. Further, exhaust gases are highly oxidizing; material environmental resistance will be an important factor for long life.
A problem, however, in spite of the excellent properties of MMC, is that micro cracks or cavities, after long term high temperature and pressure exposure, will develop in the binder. These micro cracks or cavities cause erosion and loss of binder material in the MMC. As more and more binder are lost, ceramic particles in the binder will, successively, disengage from the binder and strength and wear resistant of the MMC will accordingly decay.